Electron beam (e-beam) devices, such as e-beam defect review (eDR) instruments, are utilized for inspection or review of a target substrate, or a specimen held by the substrate. E-beam devices can include a beam separator having one or more electrostatic deflectors for deflecting a beam of primary electrons away from an optical axis normal to the substrate, or for redirecting a deflected beam into the optical axis. Electrostatic deflectors apply a voltage to multiple electrodes, thereby generating an electric field for deflecting the beam. Commonly known in the art for electrostatic deflection is the symmetric quadrupole, in which four electrode plates are spaced 90 degrees apart for deflection of the beam in either an X-direction or a Y-direction. For example, voltages +Vx and −Vx can be applied to the first and third electrodes respectively (the first and third plates opposed on the X-axis). Similarly, voltages +Vy and −Vy can be applied to the second and fourth electrodes respectively (the second and fourth plates opposed on the Y-axis).
However, an electrostatic deflector of symmetric-quadrupole configuration may not provide optimal uniformity of the electric field. Poor field uniformity may lead in turn to image degradation and performance loss in eDR use cases. An octopole electrostatic deflector, having four pairs of opposing electrodes rather than two, may provide better field uniformity than a symmetric quadrupole. However, the added complexity of the octopole requires eight voltage channels, where the symmetric quadrupole requires only four, rendering the octopole more expensive to manufacture. It may therefore be desirable to provide a more uniform deflection field while simplifying the overall system architecture of the e-beam device.